1. Field of the Invention
The present invention relates to a power circuit of an AC power supply.
2. Description of the Related Art
Referring to FIG. 1, a block diagram of a conventional AC power supply circuit is shown. An output procedure generated from a structure of the power circuit is described as follows. A power input unit 1 receives an outer AC voltage. The power input unit 1 is connected to an AC/DC converter 2 and converts the AC voltage provided from the power input unit 1 into a DC voltage via a filter and rectification.
The DC voltage output from the AC/DC converter 2 is converted by a stable power of a primary side circuit 3 and sent to a transformer 4 for being transformed. The transformer 4 includes a set of primary winding 5 and two sets of secondary windings 6. The primary winding 5 is electrically connected to the primary side circuit 3. The voltage transformed by the transformer 4 is output via the secondary windings 6. The secondary windings 6 are respectively connected to a secondary side circuit 7 thereby supplying a full-wave rectified DC voltage. The full-wave rectified DC voltage is respectively amplified by two amplifiers 8 connected to the secondary side circuits 7, and converted into a sinusoidal output AC voltage.
The amplifiers 8 are further connected to a switch circuit 9 thereby controlling contactors of the switch circuit 9 to close the contacts P1, P2, while S1 and S2 are opened, which allows the amplifiers 8 to be connected in parallel. The switch circuit 9 is able to control the connecting sequence and position, so that the contactors of the switch circuit 9 closed the contacts S1, S2, while P1 and P2 are opened, and the amplifiers 8 are connected in series. Therefore, the series and parallel circuits of the output terminal of the amplifier are switched via the contactors of the switch circuit 9 so as to adjust different AC voltages output from the AC power supply.
The AC power supply power circuit attains the purpose of supplying different AC voltages by switching the parallel-series output of the output terminal of the amplifiers. Since the AC power supply power circuit outputs different AC voltages via a plurality of parallel-series connections of the amplifiers, a complicated circuit and an increasing cost are caused. Moreover, the operation of parallel-series connection is switched by contactors but not the stepless adjusting output mode, so the contact connecting sequence of contactors of the switch circuit has to be controlled when switching and outputting different AC voltages for avoiding a short circuit. In this manner, the voltage output needs to be interrupted, which renders the transmitted power level unable to be switched promptly. The most popular industrial application of AC power supply is an AC power source manufactured by Keysight corporation. AC VOLT RANGE Selections can be 150V or 300V range in AC mode and 200V or 400V range in DC mode. The actual range values may be different depending on the configuration. It is noted that the voltage range is coupled with the output relay state. If the output relay is closed, the voltage range cannot be changed
Referring to FIG. 2, another conventional AC power supply power circuit which substantially has a similar structure to the previous AC power supply power circuit is shown. The improved power circuit is characterized in that the switch circuit 9 is connected to the secondary side circuit 7, and only one amplifier 8 is connected to the switch circuit 9 in this AC power supply power circuit.
An output procedure of the AC power supply power circuit is described as follows. The power input unit 1 receives the AC voltage supplied from the outside. An AC/DC converter 2 converts the AC voltage processed by a filter and rectification into a DC voltage. The voltage is output from a primary side circuit 3 to a transformer 4 for being transformed and becomes a full-wave rectified DC voltage via the secondary side circuits 7. Different DC voltages are output by the switch circuit 9 which switches the parallel-series connection of the secondary side of circuits 7 and transmitted to the amplifier 8 for being amplified and converted into a sinusoidal output AC voltage. In other words, the AC power supply power circuit makes use of the switch circuit 9 switching the parallel-series connection of the power terminal of the amplifier 8 for outputting different AC voltages.
The above AC power supply power circuit may simplify the circuit thereof and omit one of the amplifiers. However, since the switching operation of the parallel circuit and the series circuit of the switch circuit relies on the contactors but not on a stepless adjusting output mode, the switch circuit must be switched when the output is shut off to change the parallel and series connections of the power terminal of the amplifier for the voltage adjustment when the AC power supply switches and outputs different AC voltages. Therefore, the conventional design causes the inconvenient operation of the AC power supply and needs an improvement. A well known such AC power supply has been manufactured by California Instruments. The output of the DC converter is automatically selected for 250 VDC or 500 VDC output depending on whether the low range output (150 Vac) or high range output (300 Vac) is selected. The 250/500 VDC range selection is made by a relay that selects one of two taps on the DC output. The input/output board holds a lot of the large components and provides interconnection between the AC input, the DC-DC board, the AC power board and the output without the use of heavy cables. The output relay and the output current metering circuit are also mounted on this board. The conventional AC power supply circuit always require a relay for outputting the required AC power. The circuit board of these power supply may be programmed to have a fixed voltage range. Relays are required to switch off the circuit while the output power is to be changed. There is a conventional Programmable Precision High Power DC Power Supply which has 13 models of wide voltage range for same output power. An example is shown in below table.
Sorensen SGI seriesModelVoltageCurrent Power (kW)SGI 30X501 3050115SGI 40X375 4037515SGI 50X300 5030015SGI 60X250 6025015SGI 80X188 8018815.04SGI 100X15010015015SGI 160X94 1609415.04SGI 200X75 2007515SGI 250X60 2506015SGI 330X45 3304514.85SGI 400X38 4003815.2SGI 500X305003015SGI 600X256002515
Referring to FIG. 3, a schematic view of the outputting power level of the conventional AC power supply in switching is shown. The AC power supply power circuit supplies a low-voltage power by the parallel input of the power terminal of the amplifier. The AC power supply power circuit supplies a high-voltage power by the series input of the power terminal of the amplifier. In low-voltage power supply, the power terminal of the amplifier parallelly inputs the power supply of the low voltage and high electric current. In high-voltage power supply, the power terminal of the amplifier serially inputs the power supply of the high voltage and low electric current. The power level is unable to be switched promptly in switching, that is to say, the voltage stops outputting in switching. Therefore, it may cause a great distorted error while stopping outputting. Hence, the AC power supply power circuit is restricted and has the above-mentioned disadvantages.
In terms of that, the inventor of the present invention holds the spirit of trying for the best with the experiences of devoting to the professional development, manufacture, and marketing of the electronic equipments and the related components, thereby improving the disadvantages of the conventional AC power supply power circuit.